But a 'selfie' of the rapper - which emerged as part of a video montage and has since gone viral - is being dismissed out of hand by the first police officer on the scene of the shooting, who tells DailyMail.com he knows Tupac is dead.
Chris Carroll, who is now retired, witnessed the 25-year-old, bleeding heavily, slip into unconsciousness after saying his last words to the cop: 'F* you.'
Shakur was declared six days later without ever regaining consciousness and Carroll tells DailyMail.com he knew instantly that there was no hope.
The shooting of the rapper, on 7 September 1996, has been surrounded by conspiracy theories ever since.
They include claims that Marion 'Suge' Knight, who was beside Shakur in the car when he was shot, had ordered the assassination - and that Carroll was involved, or even that he helped Shakur flee to a new life by using a look-a-like corpse to fake his death.
The picture seemed to fuel the claim that Tupac had survived in secret.
But Caroll, 51, says that is untrue, and also says he does not believe Knight ordered the hit, while warning that the most notorious of the rap murders may never be solved.
'Tupac is dead. I saw him lose consciousness and lose his life 20 years ago,' he said.
'I still find it astonishing that fans and people believe that Tupac is alive.
'This new video does nothing to change my mind. There are lookalikes all over the world and this may be another one or a hoax.'
Carroll was on routine patrol on his cycle when he heard a radio alert about shots fired into a BMW from a white Cadillac a mile from where he was.
He was in fact just yards away as the BMW - driven by Knight - crashed into a divider at the corner of Las Vegas Boulevard, and Harmon and Carroll were on the scene instantly.
Shakur had been shot four times and Knight had sped away from the scene, followed by other cars in his entourage.
'There were about five cars in the entourage and as they began getting out of the cars I knew these were not normal citizens,' he told DailyMail.com.
'So as they got out I had my gun drawn, so I told them all to get down and stay back. They all looked edgy, and I was concerned that may be a threat or could even just run away.
'But then in the BMW through the passenger window I saw a silhouette of a guy, who was not moving.
'My immediate concern was that he could be armed and perhaps wanting to attack me or was the shooter. In the middle of this chaos was Suge, who you cannot miss, as he is this huge figure, very tall, wide and looking to come towards me.
'And to make matters even more concerning, blood was gushing out of his skull where he had been hit by a bullet.
'I told him to stay down and approached the passenger door, where Tupac was slumped, but moving slightly seemingly looking forward through the windscreen.
'I kept repeating for him to get out of the vehicle, but he didn't respond.
'I told the others to get down and I walked up to the door - I reached out for it with my left hand and had my gun in my right in case he would shoot.
'There was barely any movement from Tupac and I could see multiple bullet holes in the window and side door.
'The door was tough to get open, perhaps where it had been damaged by bullets, but after several attempts I got the door open.
'Tupac just flopped out onto my left arm. as I hadn't realized he was leaning against the door.
'I then cushioned him down to the floor. Tupac was grimacing in pain, looking panicked and gasping for breathe.
'His torso was shot up pretty bad with blood pouring from his chest out through his shirt onto his gold chains. The blood loss was vast and it curdled around the chains, clinging to them.
'As he was fading, Suge kept shouting and screaming "Pac, Pac", and then in the corner of my eye I could see him come closer.
'I warned him to stay back.
'Instantly I realized that the victim was Tupac, gasping for air and then gurgling, most likely from the blood filling his throat and lungs.
'At that moment my gut instinct told me that he was in serious trouble. I thought about first aid, but his situation was beyond me saving him - the multiple gun wounds, loss and his rolling eyes meant only trauma specialists could save him.
'Tupac was losing his fight, but he kept looking at Suge, who was growing more frantic and screaming at him.
'At this stage I felt that he was unlikely to survive, so I attempted to take a dying declaration from him.
'I asked him "Who shot you? Who did this? What happened?" repeatedly.
'Tupac didn't even acknowledge that I was talking to him, as he was staring at Suge over my shoulder.
'Then he finally moved his line of sight from Suge, glared at me, mustered the energy to take as deep as breath as possible and said, 'F* you.'
'His eyes rolled back, and then he started gargling and choking before he looked back at Suge.
'However that burst of energy proved too much, and his body physically quit, he went limp, his eyes closed half way, stopped breathing and he lost consciousness.'
Carroll says that is all the proof he needs that Tupac is dead.
'As soon as the ambulance got there, he had already lost consciousness, he was intubated immediately and taken to the local trauma center. And for all practical purposes, he was really dead when he arrived there. We have one of the best Trauma team' in the States, if not the best, but they knew he was gone.